Portal hypertension is a syndrome accounting for significant morbidity and mortality in patients with liver cirrhosis. However the molecular events within the liver endothelial cell which contribute to hepatic vasoconstriction and ensuing portal hypertension remain unknown. Thus, the Overall Objective of this program is to understand the underlying biological control mechanisms of hepatic endothelium and the pathobiologic processes leading to portal hypertension. In this regard, Preliminary Studies have 1) established the vital role of endothelial nitric oxide (NO) synthase (eNOS) derived NO in the regulation of hepatic vasodilation, 2) identified a deficiency of hepatic eNOS activity and NO production as a key pathogenic mechanism in the development of portal hypertension, and 3) determined that two eNOS binding proteins, dynamin-2 and caveolin-1 regulate eNOS catalysis in normal and portal hypertensive liver through specific protein-protein interactions. These studies have led us to formulate the Central Hypotheis that the molecular regulation of eNOS through its associated proteins, dynamin and caveolin, plays a vital role in hepatic vascular control and the development of portal hypertension. Thus the Specific Aims of the proposal are to: FIRST, establish the mechanistic role of the NOS associated protein, dynamin-2, as a positive regulator of intrahepatic vasodilatory signaling by testing the hypothesis that binding of dynamin with eNOS augments eNOS catalysis and NO production and SECOND, elucidate the mechanistic role of the inhibitory NOS associated protein caveolin, in mediating intrahepatic vasoconstriction and portal hypertension by testing the hypothesis that enhanced binding of caveolin with eNOS diminishes hepatic NO production. To address these Aims, we will utilize a variety of feasible and validated, biochemical and molecular approaches, both in vitro and in vivo. It is anticipated that these studies will further delineate the regulatory mechanisms of eNOS derived NO as they relate to hepatic vascular biology and portal pressure regulation, and thereby progress our understanding of the pathogenesis and treatment of portal hypertension.